Effectiveness of drainage of agricultural land by closed drainage in climatic conditions of the Novgorod Region

The objects of this study are closed drainage systems having a hydraulic connection of arable horizon with a drainage pipe. Experimental plots are located in the Novgorod region on sod-podzolic loamy soil. In the experiment we used such kinds of design as a standard construction with filling the drainage trench with sand-gravel mixture to the arable horizon, and a construction in the form of two-tiered drainage. The distance between drains is 14 m, the depth is 1.1 m. The design of two-tiered drainage provides for the upper tier of cavity- free drains with a depth of 0.5 m, a distance between the drains 6 m, located perpendicular to the lower tier. As a result of the study of dynamics of groundwater and soil humidification, we found out that in the experimental systems of two-tiered drainage in excessively wet years, groundwater had not risen into the topsoil during the entire growing period. Formation of groundwater after heavy rainfall was more intensive in the two-tiered drainage systems. The most favorable water-air regime in the years with different precipitation conditions (both in dry and abnormally wet years) was provided by the experimental two-tiered drainage systems with a smaller amplitude of fluctuations in moisture reserves in a soil arable layer which allowed us to conclude that draining of collectors was more effective on the base of the twotiered drainage.